Apparatus and process for change-over in continuous metal coating lines



Apnl 21, 1964 P. J. WHITLEY 3,130,068

APPARATUS AND PROCESS FOR CHANGE0VER IN CONTINUOUS METAL COATING LINES Filed March 30, 1960 E15 INVENTOR.

PAUL J. WH/TLEY;

al lewv ATTORNEYS United States Patent APPARATUS Ahll) PRGiIESS FQR CHANGE- EVER TN CGNTHIUQUS IVEETAL COATHNG LENES Paul Ii. Whitley, Middletown, Qhio, assignor to Armco it e el Corporation, Middletown, Ohio, a corporation of Filed Mar. 30, was, Ser. No. 18,629 7 ((11. 117-515} This application relates to the continuous coating of strip metal with molten metal of a different character. The invention Will be described in connection with the continuous coating metal and apparatus set forth in Patents 2,110,893, dated March 15, 1938, 2,136,957, dated November 15, 1938, and 2,197,622 dated April 16, 1940, all in the name of Sendzimir.

In an exemplary procedure under these patents, cold rolled ferrous strip is first cleaned by chemical means, including wetting and drying, or by being passed through a short oxidizing furnace which also has the efiect of removing from the surfaces of the strip the cold rolling lubricants, and other oxidizable impurities. In either procedure, a thin uniform film of oxide is formed on the surfaces of the strip. The strip next passes through a reducing furnace of substantial effective length, the furnace being provided with suitable heating means and filled with reducing gases. At the exit end of the reducing furnace there is a cooling hood through which the reduced strip passes, and in which the temperature of the strip is lowered to a temperature substantially corresponding to the temperature of the molten metal with which it is to be coated. The cooling hood is provided with a down-turned snout which dips beneath the surface of the molten coating metal in a suitable coating pot. Thus, the reduced strip is protected from reoxidation until it comes into contact with the molten coating metal, and the use of flux is obviated. The strip has a short path of travel in the coating pot and emerges therefrom in an upward direction through exit rolls or other devices designed to affect the thickness and distribution of the coating. The operation is continuous, to which end coils of the cold rolled steel are decoiled at the entrance end of the line, and the trailing end of the metal in one coil is welded or otherwise connected with the leading end of the metal in the next coil.

The practice of the invention is not necessarily confined to the process and apparatus to which reference has just been made; but it is of value in any coating process in which strip metal is passed through any elongated furnace, a cooling hood, and a snout through which the metal may be led beneath the surface of a bath of molten coating metal without IB-GXPOSUIC to atmospheric air.

The primary problem to which this invention is addressed is the problem of change-over when it is desired to coat the base metallic stripwith a difierent molten coating metal; and the basic object of the invention is the provision of a means and method by wmch such change-over can be efiected rapidly and without excessive expense. The invention is useful also both in instances where a change in the anlysis of the coating metal must be made rapidly, or where apparatus must be replaced.

The ancillary objects of the invention can best be explained, or will be apparent to the skilled worker in the art in the light of the disclosures which follow; and the various objects of the invention are attained by the use of that apparatus and procedure of which an exemplary embodiment will now be described. Reference is made to the drawings which accompany this application and in which:

FIG. 1 is a schematic diagram of the hood end of a continuous coating apparatus including the coating pot,

3,130,068 Patented Apr. 21, 1964 "ice the so-called coating machine, and associated apparatus, including holding pots.

FIG. 2 is a transverse sectional view of a snout device useful in the practice of the invention.

It will be understood that the invention is useful in changing the line for coating with a different molten coating metal, but that the specific nature of the molten coating metal employed in any one operation is no limitation on the invention. Thus, the molten coating metals may be zinc, zinc containing a small amount of aluminum, tin, aluminum and aluminum alloys, terne, and the like. For convenience herein, the use of the apparatus will be described in connection with changing the operation of the line from the use of a molten coating metal consisting mainly of Zinc to a molten coating metal consisting mainly of aluminum.

A number of serious problems are involved in a change-over from one molten coating metal to another. In general, when such a change-over is to be made, both the coating pot and the coating machine have to be changed. The term coating machine, as used herein, contemplates the exit rolls and such other devices, as for example scrapers, which may be employed in controlling the thickness and nature of the coating, and which are arranged to act upon the surface of the strip concurrently with its emergence from the exit surface of the molten coating bath, or just before, or just after its emergence. These devices are generally mounted in end frames which are held apart by rods. In some instances the reversing roll around which the strip passes within the bath will be included in the coating machine. Some coating machines also include gearing \by which the exit rolls or other rolls may be driven. it may be noted that coating machines can generally be disassembled from around the strip when they have been raised from the molten coating pot. Since coating machines, although well known as such, may take various forms, they have not been detailed herein. As has been indicated, when the nature of the molten coating metal is changed in kind, rather than in the content of a minor alloying ingredient, the coating pot and the coating machine have to be changed also. The term coating pot, as used herein, is intended to embrace the actual Vessel in which the coating metal is maintained in molten condition, whether that be a single unitary vessel, or a liner for an outer element which may or may not have to be changed. It will be understood by the skilled worker in the art that in most instances the pot will be a single unitary vessel which extends into a refractory-lined pit, there being heating elements located between the pot and the refractory walls of the pit. However, the coating pot may be a refractory vessel heated electrically by induction.

One reason why a change in the coating pot and in the coating machine becomes necessary when the coating metal is changed is that it is very difficult, if not impossible, to clean a pot completely from all traces of the first used coating metal, and in the case of a metal pot, from alloys of the metal of the pot and the machine ele- ..ents with the molten coating metal. If such cleaning is not effected, the new coating metal becomes contaminated with the coating metal first used. But beyond this, the preferred base material for the coating pot and coating machine when using zinc, by way of example, is different from the preferred base material when using aluminum. For zinc coating, a standard so-called fire box steel pot or liner is most acceptable. For aluminum coating, however, a cast iron or meehanite cast iron pot or liner is used; and similar changes in the metal employed for the coating machine are generally found necessary. in other instances, an induction heating type of coating pot having a ceramic lining may be used; and it would be substantially impossible to clean a ceramic lining of all traces of the formerly used coating metal.

The practical art has recognized the problem but has not provided an adequate solution for it. It has been suggested that a plurality of pots might be located or fastened together in adjacent positions and mounted on rails or some other sliding device so that a selected one of the pots could be moved into active position at will. It would be difficult or expensive to provide sliding alternative coating pots in connection with any suitable pit containing heating means. But a coating pot containing molten metal in modern continuous coating lines will weigh on the order of 80 to 100 tons. If full pots were to be moved, the greatest precautions would have to be taken to avoid the danger and losses inherent in the splashing of the molten coating metal.

It has also been proposed to provide two pots and two coating machines in line with each other in the direction of movement of the strip. But the use of such an expedient is time-consuming and expensive because when a change-over is made from a first to a second pot, it is necessary to extend the exit end of the hood.

As a consequence, it has hitherto been necessary, when a change-over is to be made, to bail out the coating metal from the pot and pig it so as to save it for future use. The furnace has been degassed and the snout of the cooling hood has had to be taken off so that the pot could be removed from the pit. A new pot or liner has to be placed in position and new coating metal has had to be placed in the pot or liner and melted therein. The snout has had to be replaced. The furnace has had to be regassed and brought to a temperature suitable for coating with the new metal, and the whole apparatus has had to be rethreaded, since it was not possible to perform these changes without severing the strip. Thus, in the past a change-over operation has taken a minimum of five days, and usually much longer, for changing from zinc coating to aluminum coating, and a minimum of four days to change from aluminum coating to zinc coating. The extra time in the first change is required by the duration of the heating involved in melting aluminum in the coating pot. Since normal production with a modern coating line may be 30 tons or more an hour of the coated product, it will be seen that the time lost alone in a change-over operation is of great importance.

By the use of the present invention, it has been found that a change-over from Zinc coating to aluminum coating or vice versa can be accomplished in a much shorter time, and with normal variations, can be depended upon to cut shut-down time at least in half.

Briefly, in the practice of the invention, at positions conveniently adjacent a coating pot and pit, holding pots are provided. Each of these pots has means in connection with it whereby it can be heated so that coating metal can be kept molten in the holding pots. There will preferably be a holding pot for each type of metal to be used in coating and with respect to which a change-over will be desired. Thus, there may be a holding pot reserved for aluminum, another holding pot reserved for zinc; and by the same token these holding pots may be made of metal which is non-reactive, or only slowly reactive with the particular molten metal which the holding pot is designed to contain.

The coating pot will be connected by a conduit including a pump to the holding pot which is to receive the coating metal. This need not be a permanent connection, since the pump may be connected to a pipe which can be thrust into the coating pot to a position near its bottom. The molten coating metal is rapidly transferred from the coating pot to the holding pot where it can be maintained in molten condition as desired.

Concurrently with the emptying of the coating pot, the furnace will be degassed and an end portion of the snout will be disassociated with the strip. The coating ma- 4 chine can be raised and disassociated with the strip, all as will be hereinafter more fully described.

The pot, now in empty condition, can readily be removed from the pit and a new pot or liner installed. When this is accomplished the new type of coating metal, which meantime has been held in molten condition in another holding pot, is pumped into the coating pot. A new snout end will be associated with the strip and attached to the permanent snout portion of the end of the hood. The new coating machine, which will preferably have been preheated in an adjacent furnace, will be associated with the strip and lowered into the pot. It is advantageous to provide a melting apparatus from which molten metal can also be transferred to the pot so that if the coating pot is not adequately filled from the holding pot, any discrepancy can be made up rapidly. As soon as the molten metal reaches and closes the new snout end, the furnace may be regassed. It is not necessary to sever the strip ahead of the furnace at any time, nor to withdraw the strip from the furnace, cooling hood or main snout portion. Consequently, no rethreading of these apparatus portions is required. As soon as the furnace has been regassed, the coating process can commence. It is not required to permit the furnace to cool down to room temperatures, although it is good practice to reduce the heat in the furnaces during the change-over.

Referring to the drawings, the index numeral 1 designates the end of the cooling hood attached to a reducing furnace 1a. The strip 2 passes through the hood and, changing direction over a turn-down roll 3, passes through a snout 4, the lower end portion of which dips beneath the surface of a body 5 of molten coating metal in a coating pot 6. The snout keeps the entrance portion of the coating bath free of oxide so that no flux need be used. It will be understood that the strip 2 in the preferred process, bearing a thin and uniform film of oxide as it enters the reducing furnace, has this film completely converted to iron by reducing gases in the furnace and the cooling hood. These reducing gases are generally introduced into the apparatus through ports, one of which is located at 7 at the end of the hood, and another of which is located at 8 near the lower end of the snout. The reducing gases travel through the snout, the hood, and the reducing furnace in countercurrent to the strip 2. In the preferred procedure, they issue from the entrance end of the reducing furnace where they may be burned in air.

The strip 2 will be heated to desired temperatures for reduction and annealing in the reducing furnace, and it will be cooled in the cooling hood and snout to a temper ature close to that of the molten metal in the bath 5 Thus the strip itself may add heat to the bath, and assist in keeping the metal molten, as in a galvanizing procedure. As is well understood in this art, and standard practice when coating with aluminum, it is usual to locate the pot 6 in a pit and provide heating means surrounding the pot. These have not been illustrated in the drawing.

The coating machine has not been detailed in the drawings; but a pot roll is indicated at 9, around which the strip turns so that it may exit from the bath in a substantially vertical direction, and a pair of exit rolls has been indicated at 10. In the light of the explanation above, it will be understood that these elements generally constitute part of the coating machine which will also include end frames and other suitable instrumentalities.

A holding pot has been indicated at 11 which may be connected to the coating pot 6 by suitable conduits through a pump 12. If desired, a portable pump and conduit assembly may be used. In the installation contemplated in this invention there will be at least one other holding pot 13 which can be connected to the coating pot 6 through conduits, including a pump 14. The specific positioning of the holding pots 11 and 13 is not intended to be indicated by the drawings since this is a matter of factory lay-out, and can be varied as desired. The holding pots, usually located in their own pits, will be provided with heating means suitable for maintaining the metal in them in a molten condition. These are diagrammatically shown in the drawings at 11a and 13a, respectively.

Assuming that coating has been carried on with a zinc metal in the coating pot 5, and that a change-over is desired, the first operation will usually be to degas the furnace. The reducing gases will be turned oil at the ports 7 and 8. A safety port 15 will be opened near the end of the hood, and the reducing gases issuing from this port will be ignited so as to burn in the air. This may be done by means of an electric glow unit 16, or in some other way. In this fashion, the furnace may be emptied of the reducing gases. Alternatively it is possible to flush the reducing gases from the furnace with an inert gas like nitrogen. The strip travel may be at first slowed and then stopped entirely.

The pump 12 will be used to transfer the molten metal 15 from the coating pot 6 to the holding pot 11.

The lower end of the snout is formed as a separate fitting 17. As shown in FIG. 2, this fitting may have two longitudinal parts, 17a and 17b, which are provided with lateral flanges 18 and 19. The lower end of the permanent portion of the snout and the upper end of the snout extension 17 are provided with mating flanges 20 and 21. While the flanges may be joined in any suitable way, since absolute gas tightness is required in the apparatus, it is preferred to weld them together as by arc welding or torch welding. When it becomes necessary to detach the snout extension 17, the welded edges of the mating flanges may be cut ofi by means of a cutting torch or otherwise.

The coating machine will be raised from the pot 6 and can be disassembled from around the strip. If both the snout extension and the coating machine are disassembled from about the strip, it is not necessary to cut the strip at all. However, the strip can be cut beyond the coating machine, and in this event the coating machine and the snout extension may he slipped off the cut end of the strip. The strip can easily be rejoined in the open, and rethreading of the furnace, the cooling hood and the snout will still be avoided.

When the coating pot 6 has been emptied of its charge of molten metal, the coating pot 6 may be lifted from the pit and set aside. A new coating pot or pot liner may next be installed in the pit. If it is desired now to coat the strip with aluminum, the material of the new coating pot will be suitable for that purpose. A new snout extension can now either be assembled about the strip or slipped over the cut end of the strip, and attached to the permanent portion of the snout. The material from which the new snout extension is made will likewise be suitable for contact with molten aluminum. A new coating machine, also of material suitable for contact with aluminum, will be taken from a preheating furnace 22, and either assembled about the strip 2 or slipped over the cut end of it, and then lowered into the pot.

Meanwhile, aluminum coating metal has been melted or maintained in molten condition in the holding pct 13, and it can now be transferred rapidly to the new coating pot by means of the pump 14. Any additional quantities of aluminum required to raise the metal level in the coating pot to the desired height can be added from a melting pot 23 by means of a pump 24. As soon as the molten metal closes off the lower end of the snout extension, the furnace may be regassed.

After degassing the furnace hood and snout, these elements will have become filled with air, whether or not an inert gas has been used. It will be usual to close the port 15, open the ports 7 and 8 (which will now have been connected to a source of reducing gases), and then ignite the reducing gases within the cooling hood as by means of electric glow units 25. As the reducing gases fill the snout, cooling hood, and furnace, a flame will travel through these elements in the order named, burning out any remnants of oxygen in them. Thus, the snout, the

cooling hood and the furnace will presently become completely filled with the reducing gases.

It is possible in regassing the furnace to drive the infiltrated air out of it by a second application of an inert gas, such as nitrogen, which may be introduced through the ports 7 and 8 before these ports are connected to the reducing gas supply. In the event this is done, it may be necessary, upon regassing the furnace, merely to drive the nitrogen out of the apparatus by means of the reducing gases. By either procedure, however, the furnace may be degassed and regassed without danger of explosion. As soon as the furnace, hood, and snout have been completely filled with the reducing gases, the furnace heat may be turned up, and the coating operation commenced upon resumption of the travel of the strip.

It will be realized from the above description that during the change-over operation, a change may readily be efiected in all of the metal parts of the apparatus which are to come into contact with the new molten metal. If coating is to be resumed with molten metal of the same kind but dilfering in minor alloy content, e.g. from substantially pure aluminum to aluminum containing silicon, a change of the snout extension and the coating machine may not be necessary; but the steps of the process will otherwise be the same. Conversely the invention is useful whenever it is desired to replace pots, coating machines, snout extensions or the like, or when the removal of a pot becomes necessary to permit repairs in the pit.

The operations are relatively simple and, as indicated above, may be accomplished within a comparatively short time interval. The order in which the operations hereinabove described are conducted may be varied as desired by the operator. It is not necessary to disassemble and reconstruct any portion of the reducing furnace or of the cooling hood, or the permanent part of the snout, and the disassembly and reassembly of snout extensions does not occupy a great length of time. No rethreading of furnace apparatus is necessary. Consequently, a considerable degree of heat may be maintained in the reducing furnace so that a long heating-up period is obviated.

It will be understood that as many of the holding pots may be provided as are required for the number of different coating metals which are to be used in the unit. Similarly, a melting pot such as 23 may be provided for each type of metal to be employed. If coating operations are to be carried on for a long time with any given coating metal, so that it becomes uneconomical to maintain another coating metal molten in its holding pot, it is possible to withdraw that metal from the holding pot by means of the appurtenant pump and pig it for storage without interrupting either the coating operation or the change-over operation.

The apparatus has been illustrated diagrammatically, and may be varied in design. For example, when coating with aluminum, the design of the snout extension may be varied to permit the use of the scavening means and method taught in the Oganowski Patent 2,437,919.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in an exemplary embodiment, what is claimed as new and desired to be secured by Letters Patent is:

1. A process of effecting rapid change-over from one molten coating metal to another in a continuous coating apparatus comprising a reducing furnace, a cooling hood, and a snout, an end of which clips into molten coating metal in a coating pot so that a strip of metal passing through said elements will be coated in said pot and will exit therefrom through a coating machine in said pot, said furnace, said cooling hood, and said snout being filled with a reducing gaseous atmosphere, which process comprises the steps of rapidly pumping molten metal from said pot into a supplementary holding pot, degassing said furnace, cooling hood, and snout, removing the said pot and replacing it with another pot, removing a detachable end of said snout, and replacing it with another detachable end, removing said coating machine and replacing it with another coating machine, all without dethreading said furnace, said cooling hood, and said snout, pumping molten metal from another source into said replaced pot, and regassing said furnace, said cooling hood, and said snout.

2. An apparatus for facilitating the rapid change-over from one coating metal to another in a continuous metal coating line wherein strip to be coated is passed from a reducing furnace through a cooling hood to a coating pot holding a bath of coating metal, said cooling hood terminating in a snout extending into the bath of molten coating metal, a first supplementary holding pot for molten metal, heating means in connection with said first supplementary holding pot, conduit means including a pump for rapidly transferring molten metal from said coating pot to said first supplementary holding pot, whereby to remove a first coating metal from said coating pot, a second supplementary holding pot having heating means in connection therewith for maintaining a molten supply of a second coating metal to replace said first coating metal upon the emptying of said coating pot, and conduit means including a pump for rapidly transferring said molten second coating metal from said second supplementary holding pot to said coating pot, thereby readying said coating line for continued use with a different coating metal.

3. Apparatus as claimed in claim 2 including means for rapidly emptying said furnace, said cooling hood, and said snout of combustible reducing gases.

4. An apparatus for facilitating the rapid change-over from one coating metal to another in a continuous metal coating line wherein strip to be coated is passed from a reducing furnace through a cooling hood to a coating pot holding a bath of coating metal, said cooling hood terminating in a snout entering into the bath of coating metal, a first supplementary holding pot for molten metal, heating means in connection \m'th said first supplementary holding pot, conduit means including a pump for rapidly transferring molten metal from said coating pot to said first supplementary holding pot, whereby to remove a first coating metal from said coating pot, a replacement coating pot, a second supplementary holding pot having heating means in connection therewith for maintaining a molten supply of a second coating metal to replace said first coating metal upon the emptying of said coating pot and the replacement thereof with said replacement coating pot, said snout terminating in a removable end which may be removed and replaced along with the coating pot, and conduit means including a pump for rapidly trausferring said molten second coating metal from said second supplementary holding pot to said replacement coating pot, thereby readying said coating line for continued use with a different coating metal.

5. The apparatus claimed in claim 4 wherein the removable end of said snout comprises a fitting having two longitudinal parts each provided with mating lateral flanges adapted to be joined together in gas tight condition, as by welding, whereby when it is desired to remove and replace said fitting, the welded edges of the mating flanges may be cut oil so as to separate the longitudinal parts for removal without disturbing the metal strip.

6. Apparatus as claimed in claim 2 including a coating machine comprising a reversing roll positionable in said pot and exit rolls for controlling the thickness of a molten metal coating formed on a strip passed through said apparatus, said coating machine being removable from said pot for replacement along with said pot.

7. Apparatus as claimed in claim 6 including a melting device adapted to furnish additional quantities of molten coating metal rapidly to a replaced pot, and means in cluding a pump for transferring molten metal from said melting apparatus to said pot.

References Cited in the file of this patent UNITED STATES PATENTS 2,500,041 Morey Mar. 7, 1950 2,592,282 Hodil Apr. 8, 1952 2,658,839 Talmey, et a1. Nov. 10, 1953 2,848,975 Renkin Aug. 26, 1958 2,887,087 Jones May 19, 1959 2,930,349 Jones Mar. 29, 1960 2,959,151 Ehrlich Nov. 8, 1960 2,960,963 Shelton Nov. 22, 1960 

1. A PROCESS OF EFFECTING RAPID CHANGE-OVER FROM ONE MOLTEN COATING METAL TO ANOTHER IN A CONTINUOUS COATING APPARATUS COMPRISING A REDUCING FURNACE, A COOLING HOOD, AND A SNOUT, AN END OF WHICH DIPS INTO MOLTEN COATING METAL IN A COATING POT SO THAT A STRIP OF METAL PASSING THROUGH SIAD ELEMENTS WILL BE COATED IN SAID POT AND WILL EXIT THEREFROM THROUGH A COATING MACHINE IN SAID POT, SAID FURNACE, SAID COOLING HOOD, AND SAID SNOUT BEING FILLED WITH A REDUCING GASEOUS ATMOSPHERE, WHICH PROCESS COMPRISES THE STEPS OF RAPIDLY PUMPING MOLTEN METAL FROM SAID POT INTO A SUPPLEMENTARY HOLDING POT, DEGASSING SAID FURNACE, COOLING HOOD, AND SNOUT, REMOVING THE SAID POT AND REPLACING IT WITH ANOTHER POT, REMOVING A DETACHABLE END OF SAID SNOUT, AND REPLACING IT WITH ANOTHER DETACHABLE END, REMOVING SAID COATING MACHINE AND REPLACING IT WITH ANOTHER COATING MACHINE, ALL WITHOUT DETHREADING SAID FURNACE, SAID COOLING HOOD, AND SAID SNOUT, PUMPING MOLTEN METAL FROM ANOTHER SOURCE INTO SAID REPLACED POT, AND REGASSING SAID FURNACE, SAID COOLING HOOD, AND SAID SNOUT. 